This application relates to a process for making high internal phase emulsions (HIPE or HIPEs). This application particularly relates to a continuous process employing a static mixer to produce such emulsions.
An emulsion is a dispersion of one liquid phase in another, substantially immiscible, continuous liquid phase. Water-in-oil (or oil in water) emulsions having a high ratio of dispersed phase to continuous phase are known in the art as High Internal Phase Emulsions hereafter referred to as xe2x80x9cHIPExe2x80x9d or HIPEs). At relatively high dispersed phase to continuous phase ratios the continuous (external) phase becomes essentially a thin film separating and coating the droplet-like structures of the internal, dispersed phase. In one embodiment of particular commercial interest, the continuous oil phase of a water-in-oil HIPE comprises one or more polymerizable monomers. The oil phase can be then be polymerized forming a cellular structure (i.e. a foam) having a cell size distribution defined by the size distribution of the dispersed, internal-phase droplets. Since the cell size distribution has a substantial effect on the properties of the foam, it is advantageous to be able to closely control the droplet size of the internal, dispersed phase in a HIPE being produced for that purpose.
Water-in-oil HIPEs comprising a polymerizable oil phase are known to the art. See, for example, U.S. Pat. No. 3,988,508 (Lissant), issued Oct. 26, 1976; U.S. Pat. No. 5,149,720 (DesMarais et al.), issued Sep. 22, 1992; U.S. Pat. No. 5,260,345 (DesMarais et al.), issued Nov. 9, 1993; U.S. Pat. No. 5,189,070 (Brownscombe et al.), issued Feb. 23, 1993; U.S. Pat. No. 5,827,909 (DesMarais), issued Oct. 27, 1998; and U.S. Pat. No. 5,900,437 (Mitchell, et al.) issued May 4, 1999.
For production of HIPEs, the art has typically used mixers that use rotating elements to provide the shear necessary to disperse the internal phase throughout the continuous phase. See, for example, U.S. Pat. No. 5,250,576, issued to DesMarais, et al. on Oct. 5, 1993 and the aforementioned U.S. Pat. No. 5,827,909. While such mixers can provide HIPEs that are polymerizable into foams having desirable cell size distributions, improvements in the method of producing such HIPEs are needed. For example, it is well known that it is difficult to predictably scale mixers having rotating elements from a laboratory or pilot-plant scale to a full production scale. That is, simply increasing the size of a mixer to increase production capability (even if some process parameters, such as mixing element tip speed are matched) does not necessarily result in a HIPE having the same properties as are produced using a process designed around a smaller scale mixing apparatus. Thus there is a need for processes for producing HIPEs that can be more reliably scaled up to produce production quantities of HIPEs.
One means of applying shear that is more predictably scaleable than the rotating elements as are known to the art is the use of in-line mixers or static mixers. In such mixers fluid flow past fixed elements is divided and recombined by the arrangement of the elements to provide mixing.
The use of static mixers to form HIPEs is known to the art. For example, U.S. Pat. No. 4,844,620, issued to Lissant, et al on Jul. 4, 1989, describes a system that forms HIPEs by introducing an internal and an external phase into a recirculation loop that includes a static mixer. A small portion of the flow through the recirculation loop is withdrawn as product. While such a system may be successful in production of HIPEs, the system would be expected to produce HIPEs with an undesirably broad internal phase size distribution because at least a portion of the material in the product stream would have seen only a single pass through the static mixer. Since such single pass material would have experienced less shear the material would, of necessity, be dispersed into larger size particles. Further, if the HIPE is a water-in-oil HIPE where the oil phase is polymerizable, such polymerization would either star taking place in the recirculation loop (initiator present) or require injection of an initiator into the product stream. In either case the added process complexities are obvious.
Thus there is a further need for single pass processes that can produce HIPEs having relatively narrow size distributions. There is a still further need for Such single pass processes to be able to produce HIPEs that can be polymerized to produce HIPE-derived foams having a controlled, predictable, and narrow cell size distribution. There is also a need for single pass systems that are compatible with processes that operate at relatively high temperatures so as to accelerate such polymerization reactions.
A method of mixing two or more immiscible fluids to form high internal phase emulsions (HIPEs) comprising the steps of:
a) providing a first phase;
b) providing a second phase, wherein said second phase is substantially immiscible with said first phase and the ratio of said first phase to said second phase is between about 2:1 and about 250:1,
c) combining said first and second phases to provide a premixed process stream;
d) processing said premixed process stream using at least one static mixer segment in a single pass so as to provide sufficient shear to emulsify said first phase in said second phase creating said high internal phase emulsion having a internal phase size distribution with a mean particle size.
Preferred phase compositions, static mixer setup and the like are also described. The method of the present invention is particularly useful for preparing HIPEs that are subsequently polymerized to provide HIPE-derived foams.